It has long been known to introduce drugs into the systemic circulation system via a contiguous mucous membrane to increase onset of activity, potency etc.
For example, U.S. Pat. No. 3,560,625 disclose aerosol formulations for introducing an alkoxybenzamide into the systemic circulatory system. Two different types of aerosol formulations are disclosed:    a) fluorinated hydrocarbon type comprising 2% by weight alkoxybenzamide, 18% ethanol, and 80% propellant; and    b) nebuliser type comprising 0.5% by weight alkoxybenzamide, a mixed solvent system comprising 10.3% ethanol and 31.4% propylene glycol and 57.8% deionised water.
U.S. Pat. No. 3,560,625 identifies a problem in finding a suitable solvent system to produce an aerosol spray for inhalation of the ortho-ethoxybenzamide, due to the fact that whilst ethanol was undoubtedly the best solvent, a mixture containing more than 18% of ethanol by weight produced an unpleasant oral reaction which more than counterbalanced the efficacy of the oral route.
When the present applicant set out to produce spray formulations for a botanical drug substance comprising one or more cannabinoids they were aware that the highly lipophylic nature of the cannabinoids could present problems in formulating the active component(s).
The present applicant first sought to develop a formulation for oromucosal, preferably sublingual, delivery in a pressurised aerosol or spray form, as disclosed in international patent application PCT/GB01/01027. Their initial focus was on propellant driven systems with HFC-123a and HFC-227 but these proved to be unsuitable as solvents for the cannabinoids. The formulations comprised synthetic Δ9-THC in amounts from 0.164 to 0.7% wt/wt, with ethanol as the primary solvent in amounts up to 20.51% by weight. One particular composition comprised 0.164% synthetic Δ9-THC, 4.992% ethanol, 4.992% propylene glycol and 89.582% p134a (propellant).
The applicant found that even at ethanol levels of 20% by volume of the total formulation volume they were unable to dissolve sufficient levels of Δ9-THC in a standard spray dose to meet clinical needs, because of the cannabinoids poor solubility in the propellant. They also found that the ethanol level could not be increased, as the delivery characteristics of the device nozzle altered substantially when the lower volatility solvents were increased above a critical ratio. The HFC-123a and HFC-227 propellant sprays delivered a maximum of 7 mg/ml, whereas initial clinical studies suggested the formulations would be required to contain up to 50 mg cannabinoids/ml.
Thus, the present applicants focussed on self-emulsifying drug delivery systems, as are discussed in detail in a review article European Journal of Pharmaceutics and Biopharmaceutics 50 (2000) 179-188, which concluded that the poor aqueous solubility of many chemical entities represents a real challenge for the design of appropriate formulations aimed at enhancing oral bioavailability.
In their co-pending International application PCT/GB02/00620 the applicant discloses a wide range of cannabinoid-containing formulations containing at least one self-emulsifying agent. The inclusion of at least one self-emulsifying agent was thought necessary to get the formulation to adhere to the mucosal surface in order to achieve sufficient absorption of the cannabinoids. One particular formulation comprised 2% by wt glycerol mono-oleate, 5% CBME of G1 cannabis to give THC, 5% CBME of G5 cannabis to give CBD, 44% ethanol BP and 44% propylene glycol.